The objective of the proposed research is to clarify the role of deformability in premature red cell destruction. To achieve this, rabbit red cells will be specifically modified to alter the three factors that regulate whole cell deformability; internal viscosity, surface area-to-volume ratio and membrane visco-elastic properties. Changes in deformability of the altered cells will be assessed by ektacytometric measurements. Subsequent measurements of in vivo survival of the treated cells will then be correlated with those deformability measurements to provide a basis for understanding of how these factors, independently and in combination, can shorten red cell survival. This, in turn, should be useful in evaluating the utility of deformability measurements in the assessment of hemolytic disorders.